The first objective of the proposed research is to identify patterns of cognitive characteristics among persons with Huntington's Disease (HD) and those at genetic risk for this disorder. We will examine the clinical significance of these patterns and evaluate their utility for the early identification of the disease. This will be accomplished through the application of cluster analytic methods to standard psychological measures (Wechsler Adult Intelligence Scale and Wechsler Memory Scale). The clusters identified will be validated using neuropsychological neurologic and psychiatric data from both initial evaluation and three-year follow-up. On psychometric, neuropsychological, and neurobiologic grounds, it is proposed that attentional mechanisms are particularly vulnerable in this disorder. Our second objective, therefore, is to evaluate attentional processes in both recently diagnosed Huntington's Disease patients and in persons at-risk. Both selective and sustained attention will be studied, and the effects of concurrent perceptual and memory demands on sustained attention will be evaluated. It is predicted that persons affected with Huntington;s Disease and the subset of person at-risk with psychometric profiles most like those of HD patients will display specific defecits in attention.